Aromatic polycarbonate resins are frequently used in medical products due to their high impact resistance, heat resistance, and transparency and good safety.
For application of aromatic polycarbonates in medical products, the high-pressure steam sterilization method and the ethylene oxide gas (EOG) sterilization method have conventionally been employed. However, the steam sterilization method has disadvantages that complete sterilization is difficult and the treatment procedures have drawbacks such as the necessity of a drying step after the sterilization. Further, the EOG sterilization method has problems such as the toxicity of residual EOG absorbed in the sterilized materials.
For this reason, attention has recently focused on radiation sterilization in which products to be sterilized are exposed to radiation (generally, gamma rays and electron beams) and which can be practiced at relatively low costs under a low temperature and dry atmosphere, and also has focused on oxygen-free radiation sterilization in which products are sterilized under substantially oxygen-free conditions for the purposes of suppressing the multiplication of microorganisms and preventing the deterioration of hollow fibers made of cellulose acetate, etc.
However, polycarbonate resin molded articles conventionally used in those fields have a defect that upon exposure to radiation, the articles suffer yellowing due to the decomposition of the resin, thus lessening the value of the products. This tendency becomes very strong where the radiation sterilization is conducted under a substantially oxygen-free atmosphere.
JP-A-62-135556 discloses a composition which is prepared by blending a polyether polyol or its alkyl ether with an ordinary polycarbonate resin containing no halogen, thereby showing improved resistance to yellowing caused by irradiation. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, the improvement in diminishing the irradiation-caused yellowing is insufficient, and particularly, in a substantially oxygen-free atmosphere, almost no effects are brought about. In addition, the above-proposed polycarbonate resin composition is defective in that the addition of a polyether polyol or its alkyl ether often results in poor heat stability of the composition.